This paper presents results from a study of lava flows that were discharged by Bezymyannyi Volcano at different times, from old (about 3500 years ago) to recent ones (1985–1989). We provide detailed descriptions of the composition, structure, and petrophysical properties for the main types of constituent rocks, which are andesites and basaltic andesites. It was found that porosity is the leading factor that controls rock properties, while the effects of structural and mineralogical features are less prominent. We demonstrate the variation in the properties of rocks that compose the lava flows in relation to their ages: the older a rock is, the higher its density and strength and the lower its porosity is.